1. Field of the Invention
The present invention generally relates to advanced batteries such as used in electric vehicles (EVs) end hybrid-electric vehicles (HEVs), and more particularly, to an arrangement for internally heating such batteries for optimal use in cold climates.
2. Background Art
Generally, most electrochemical batteries, including lead acid, NiCd, NiMH, Li-Ion, or Li-Polymer, require some form of heating when used by electric, hybrid-electric, or conventional vehicles in cold climate conditions before the batteries are capable of providing full power. Traditionally, known methods of warming a vehicle battery included using an external heat generating source, such as a heated jacket or a block heater, to externally apply heat to the battery. Unfortunately, such approaches have not proven to be satisfactory because the amount of energy expended to generate the heat is relatively high compared to the small increase in the internal temperature of the battery.
In addition in hybrid-electric vehicles (HEVs), battery packs have been warmed (when being operated in subfreezing temperatures) via a battery charging process. For example, the vehicle's internal combustion (IC) engine (e.g., gas or diesel) is operated to drive an electric motor in a “generator mode” and a motor inverter in a “rectifier mode” so that the battery is charged based on energy from the IC engine. Since the impedance of the battery rises considerably in an extremely cold climate condition, the flow of electrical current through the battery as a result of the charging process inherently creates a heat byproduct capable of warming the battery internally. Such an approach will not work with electric vehicles (EVs) because of the absence of an additional power source on the vehicle.
U.S. Pat. No. 6,882,061, entitled “Battery Self-Warming Mechanism Using the Inverter and Battery Main Disconnect Circuitry” and incorporated by reference herein, discloses a battery heating arrangement that provides significant improvement over such known approaches. More specifically, the '061 patent discloses a switching arrangement that allows the output current of a DC to AC inverter circuit to be selectively directed to either an electric motor (to power the motor) or to a center tap located between battery cells (to allow the AC current to internally heat the battery). The present invention seeks to provide further improvement over such arrangements.